This invention relates to electrical switches and more particularly, though not solely, to slide actuated switches.
Slide actuated switches come in a variety of forms. A common type has a strip of conductor material mounted on a slider and fixed contacts connected to terminals of the switch mounted in a body. Movement of the slider relative to the body moves the strip of conductor material into and out of contact with the fixed contacts to provide a switching action. Such a switch has only a slow make and break and is therefore only suitable for low voltage and low current applications. Another type of slide actuated switch relies upon the slider movement causing a pivoting movement of a conductor member from one to the other of two extreme positions. In the extreme positions the conductor member makes different connections with fixed contacts. Such a switch has a xe2x80x9csnap-overxe2x80x9d action and so speeds up the make and break connection but it is still only useful with relatively low currents.
Another very common type of switch which is in widespread use is a so-called xe2x80x9cmicroswitchxe2x80x9d. Such switches normally have at least three terminals which provide a normally OFF function and a normally ON function. Such switches can include more terminals and may have a changeover function. Typically such microswitches include an actuating plunger and it is movement of the plunger into and out of the body of the microswitch which actuates the switching function. Such microswitches are quite often incorporated into push-button type switches but they can include a lever pivotally mounted on the body which engages and operates the plunger. The free end of such a lever may include a roller so that it can operate with a profiled rotary cam. Such microswitches are a commodity item and accordingly inexpensive and they can handle relatively high currents and voltages, typically 250 volts at 10 amps.
According to this invention a slider actuated switch comprises a microswitch switching mechanism including a biassed plunger mounted in a body, a slider mounted on and co-operating with the body so that it is capable of sliding backwards and forwards along the body, and a cam associated with the slider and engaging the biassed plunger as the slider is moved backwards and forwards to operate the plunger and thereby actuate the microswitch switching mechanism.
Preferably the microswitch switching mechanism is entirely conventional in construction and preferably it is of a type that includes a body formed in two parts, a first part which contains and forms part of the switching mechanism and a second part or lid. In this case the lid is modified to provide a track which constrains and cooperates with the slider to control its movement in the backwards and forwards direction.
Preferably the cam is profiled to provide an xe2x80x9covercentrexe2x80x9d action. Thus, with the slider at one extreme position of its travel the slider is either out of contact with the plunger or at least only just touching the plunger. As the slider is moved towards the other extreme of its travel the cam is profiled to engage the plunger and depress it to its fully depressed position as the slider is in the centre of its travel and then to release the plunger slightly when the slider reaches the other extreme end of its travel. In this way, the bias of the plunger has to be overcome when any attempt is made to return the slider to its starting point and consequently this prevents the slider moving under vibration alone, for example.
Typically sliding switches in accordance with this invention are stacked next door to one another to provide a gang of slider switches and, in this case, each microswitch preferably includes two tangs so that each slider switch engages the walls of a surrounding mounting frame or case holding the gang of slider switch assemblies in position side-by-side. When the switch is to be used in this fashion one side of the track formed by the lid can be entirely open to facilitate the assembly of the slider with the track and then, once a number of switches are arranged side-by-side the sliders in each switch are prevented from being removed from the track either by the neighbouring slider actuated switch or by the side wall of the mounting frame or case in which all of the slider switches are mounted.